Carrol poses an interesting riddle with this quote from Marx, but there are other quotes from Marx that raise a question about Carrol's interpretation of it.
"The anatomy of man is a key to the anatomy of the ape." Marx doesn't say that the anatomy of the ape is not a key to the anatomy of man. Then the system of phyla and taxa ,and the Darwinian idea that species descend from common ancestors would seem contradict the assertion that the "past doesn't explain the present " at all. Apes and humans are both primates and hominoidea ( I think it is). It would seem that the common ancestor is a fact from the past that explains partly the anatomy of both. But maybe there's something else.
http://www.autodidactproject.org/quote/marxsci2.html
Marx & Engels on the Science of History
We know only a single science, the science of history. One can look at history from two sides and divide it into the history of nature and the history of men. The two sides are, however, inseparable; the history of nature and the history of men are dependent on each other so long as men exist. The history of nature, called natural science, does not concern us here; but we will have to examine the history of men, since almost the whole ideology amounts either to a distorted conception of this history or to a complete abstraction from it. Ideology is itself only one of the aspects of this history.
Marx, Karl; Engels, Frederick. The German Ideology, 3rd rev. ed.
(Moscow: Progress Publishers, 1976), p. 34f. (Collected Works; vol. 5)
>From vol. 1, chapter 1, Feuerbach, section I.1.
Note: This famous passage is crossed out in the original manuscript, and thus appears as a footnote in the printed edition of the Collected Works. It is sometimes omitted both in print and in online form.